Greece has been edging towards a deal with its private-sector creditors as the hours ticked away towards Thursday's deadline for the agreement required to trigger a fresh €130bn bailout for its troubled economy.

As the standoff between the government in Athens and bondholders reached its climax, the body representing financial institutions in the talks said investors holding more than 40% of Greece's debt had now agreed to accept losses of more than 50% on their bonds.

The Private-Creditor-Investment Committee (PCIC) for Greece said the list of those institutions signed up to the deal included RBS, HSBC, Société Générale and Germany's Deutsche Bank. A statement by the PCIC gave strong backing to the private sector involvement in a Greek debt write-down necessary for it to receive financial help from the IMF, the EU and the European Central Bank.

The involvement of most Greek institutions will take the total above 50% and there was hope that the deal would ultimately secure the support of banks, pension funds, insurance companies and hedge funds that own 75% of the country's €206bn private-sector debt. That prospect helped financial markets steady after the sharp drop on Tuesday.

Reuters said it had been told by a senior source in the Greek finance ministry that the government was confident that well over 75% of eligible bonds would be submitted for a debt swap.

That would comfortably clear the 50% legal threshold for an agreement to be valid and the two-thirds cut-off point at which Greece would be able to impose a deal on bondholders through a collective action clause passed by its parliament.

But a significant minority of investors – including five small Greek pension funds – are still refusing to sign a deal. Some hedge funds have said the so-called "haircut" of 53.5% is too severe and have said they will take legal action to secure better terms. Evangelos Venizelos, Greece's finance minister, attacked the institutions and warned that they risked making their holdings worthless by their hardline stance. "If the PSI does not succeed, what will be the value of their bonds? Zero!"

The strong language from Venizelos was seen as a threat to those bondholders – amounting to 14% of the total – whose investments are held under international rather than Greek law and would therefore not be subject to any collective action clause imposed by Athens.

Analysts warned there could be a sharp sell-off in the markets in the event Greece failed to win the support of enough bondholders by the deadline.

The consultants Capital Economics said if the deal failed to attract two-thirds support "there could be a particularly adverse reaction in the financial markets as it could potentially prompt the rest of the eurozone to withdraw the bailout deal".

It added: "While some policymakers and commentators have suggested that this might not be disastrous, we think that it could have rather more serious implications and undermine confidence in policymakers' ability to prevent the debt crisis from spreading to Italy and Spain."

European policy makers are optimistic that the deal with Greece's private-sector creditors is the final hurdle in a crisis stretching back to late 2009.

The damage to 17-nation eurozone economies from the debt crisis was underlined on Wednesday by much worse-than expected data from both Germany and Spain.

Germany, the single currency's strongest economy, posted a 2.7% drop in factory orders in January, against an expected 0.5% rise. Weaker demand from overseas was held mainly responsible.

Meanwhile, industrial output in Spain – where Madrid has announced plans to slow the pace of deficit reduction in the light of fears about a looming recession – was 4.2% lower in January than a year earlier.

Simon Smith, chief economist at FxPro, said: "What really matters beyond this week is the extent to which the EU powers can convince investors that this really is a one-off. Any residual fears in peripheral eurozone nations that they could be next have the potential to be the most disruptive force going forward, and Portugal currently looks to be the most vulnerable to such perceptions."